Large-Format ASME Steam Generator Keeps Hoeganaes Hydrogen Lines Running Clean

When a world-leading metal powder producer needed a 5.2-ton steam generator capable of sustaining hydrogen reducing atmospheres at industrial scale, Lmart delivered an ASME U-Stamp vessel in Inconel 825 and Duplex 2205 — on time and to the exacting standards of Air Products’ supply chain.

End User	Hoeganaes Corporation (GKN Powder Metallurgy)
Procurement Channel	Air Products and Chemicals, Inc.
Equipment	Steam Generator PHG830
Tag / Size	DN 1772 × THK 10 × L 4482 mm
Weight	5,200 kg
Code & Stamp	ASME Section VIII Div. 1 — U Stamp
Shell Material	SB424 N08825 (Inconel 825) / Duplex 2205
Tube Material	N08825 (Inconel 825)
Application	High-purity hydrogen generation for metal powder atomisation and annealing
Industry	Powder Metallurgy / Industrial Gas

Customer Background

Hoeganaes Corporation — a subsidiary of GKN Powder Metallurgy — is one of the world’s largest and most technically advanced producers of iron and steel powders. From its manufacturing sites in the United States, Hoeganaes supplies the automotive, industrial, and sintered component sectors with atomised metal powders that demand tight chemical and physical consistency.

At the core of metal powder production is a deceptively straightforward but technically exacting requirement: a reducing atmosphere. Once metal is atomised into fine powder, residual oxide layers on individual particles must be removed before the powder can be pressed and sintered into structural components. Hydrogen is the preferred reducing agent — it reacts selectively with metal oxides, leaving behind only pure metal and water vapour. The result is powder with the surface chemistry, green strength, and dimensional accuracy that automotive Tier-1 manufacturers require.

Air Products, one of the world’s largest industrial gas companies, manages the supply, handling, and process engineering of hydrogen and related gases at Hoeganaes’ facilities. When a large-capacity steam generator needed to be sourced and fabricated for the PHG830 process train, Air Products turned to Lmart.

The Engineering Challenges

Large-Format Exotic Alloy Fabrication

At DN 1772 mm (shell outer diameter approaching 1.8 metres), the PHG830 is not a standard vessel. Forming, rolling, and welding Inconel 825 plate at this diameter demands workshop capability that goes well beyond what most pressure vessel fabricators can offer. Inconel 825 — a nickel-iron-chromium alloy with molybdenum and copper additions — provides outstanding resistance to both reducing and oxidising corrosive environments. However, its work-hardening behaviour and tight interpass temperature requirements make large-diameter shell fabrication a disciplined, time-intensive operation.

Duplex 2205 was specified for selected pressure-boundary components. The combination of Inconel 825 and Duplex 2205 in a single vessel requires a fabricator with multi-alloy weld procedure qualification and documented experience across both material families.

Hydrogen Purity is Non-Negotiable

The steam generator feeds directly into a hydrogen atmosphere circuit. Any contamination introduced through improper material selection, inadequate cleaning, or sub-standard weld quality will carry through into the annealing furnace atmosphere — degrading powder quality, causing oxide formation, and potentially causing a batch rejection. Weld quality in hydrogen service must be essentially defect-free. Internal surfaces must be free of oil, scale, and foreign material. The entire fabrication programme must be traceable and documented.

ASME U Stamp — Third-Party Witness at Every Step

Air Products’ procurement requirements mandate ASME Section VIII Div. 1 compliance and U Stamp certification for all pressure vessels in this application. This is not a "designed to ASME" arrangement — it requires an Authorised Inspection Agency (AIA) witness at defined fabrication milestones, reviewed design calculations, approved WPS/PQR records, and a stamped Manufacturers’ Data Report (MDR). For an international fabricator, managing AIA coordination efficiently is as important as the welding itself.

Why Lmart

Lmart was selected after a technical review of fabricator capabilities against the combined requirements: large-diameter Inconel 825 shell fabrication, dual-alloy (Inconel + Duplex 2205) weld procedure qualification, and a fully operational ASME U Stamp programme.

Three specific factors drove the decision:

Material handling at scale. Lmart’s workshop has the plate rolling and shell assembly capacity to handle 1.8-metre diameter shells in heavy nickel alloy plate without resorting to segmented construction or field seam welds — both of which introduce additional quality risk.

Active ASME U Stamp authorisation. Lmart maintains its ASME Certificate of Authorisation and works routinely with ASME Authorised Inspection Agencies. The internal quality system — drawing control, traveller management, NDE co-ordination, and final data book assembly — is built around the ASME Code workflow, not grafted on as an afterthought.

Alloy experience with documentation. Beyond raw welding capability, Lmart maintains qualified WPS/PQR procedures covering N08825 and Duplex 2205 base metals and their dissimilar combinations. Procedure qualification records are reviewed by the AIA as part of the U Stamp process — this is not paperwork that can be improvised after contract award.

Engineering Solution — PHG830 Design

The PHG830 steam generator was engineered as a fired or indirect steam production vessel in the large-format pressure vessel category, with the following key design parameters:

• Shell: SB424 N08825 plate, 10 mm nominal wall thickness, formed into a DN 1772 mm cylinder and longitudinally seam-welded to full-penetration radiographic quality
• Tubes: N08825 seamless tubes, expanded and strength-welded into N08825 tubesheets to prevent crevice attack in the hydrogen-wet service environment
• Duplex 2205 Zones: Applied at selected pressure-boundary connections where the higher yield strength of Duplex 2205 offered a design advantage and where corrosion service conditions permitted its use alongside the primary Inconel shell
• Overall Envelope: 4,482 mm tangent-to-tangent length, 5,200 kg finished weight
• Design Code: ASME Section VIII Division 1, with full MDR documentation and U Stamp applied by the authorised inspector at completion

All nozzle and flange connections were specified in compatible nickel alloy or duplex material to maintain corrosion continuity across the pressure boundary. Hydrotest was performed in the presence of the AIA at 1.3× design pressure prior to final surface preparation and dispatch.

Why Inconel 825? Material Selection Rationale

Property	316L SS	Inconel 825 (N08825)	Inconel 625 (N06625)
SCC Resistance	Poor — fails in chloride environments	Excellent	Superior
Pitting Resistance (PREN)	~25	~33	~51
Max Service Temp	~450 °C	~540 °C	~650 °C
Weldability	Excellent	Good — requires qualified WPS	Good — requires qualified WPS
Relative Material Cost	1×	3–4×	6–8×
Typical Application	General chemical service	H&sub2;/syngas, high-purity gas, sulfuric acid	Subsea, ultra-high corrosion

For this service — high-purity hydrogen generation with mixed acid condensate — Inconel 825 provides the required corrosion resistance at roughly half the cost of Inconel 625, making it the engineering-optimal choice.

Quality Control and Delivery

Fabrication was managed under Lmart’s ASME-compliant quality system with the following inspection hold and witness points:

• Material receipt inspection: Mill test reports verified for chemistry and mechanical properties; SB424 N08825 plate identity confirmed against ASME Section II Part B
• Fit-up and pre-weld inspection: Weld joint geometry, cleanliness, and dimensional alignment confirmed before any weld initiation
• NDE post-weld: Radiographic examination of all Category A and B longitudinal and circumferential seams; liquid penetrant examination of nozzle-to-shell welds
• Tubesheet and tube-to-tubesheet weld inspection: PT of all tube weld joints; dimensional verification of tube projection and expansion length
• Hydrostatic test: AIA witness at 1.3× MAWP; zero leakage, zero visible deformation
• Final documentation: MDR, all mill certs, NDE reports, WPS/PQR, design calculations, and ASME U Stamp nameplate recorded and delivered in a bound data book

The vessel was delivered within the contracted schedule, packaged for international freight with nitrogen blanket on tube side and full nozzle protection.

Results

The PHG830 steam generator was installed into Hoeganaes’ hydrogen atmosphere processing line and commissioned without incident. The project delivered:

• Zero weld repair on final NDE — all seams accepted first-pass
• Full ASME MDR package accepted by Air Products’ engineering team without deviation requests
• On-schedule delivery — no impact to the Hoeganaes line commissioning programme
• Material traceability covering every pressure-boundary component, from raw plate coil identity to finished vessel nameplate

For Air Products’ procurement and engineering teams, the project established Lmart as a qualified source for large-format exotic alloy pressure vessels in hydrogen and industrial gas service — a vendor category where the supply base globally is limited.

Customer Voice

Air Products selected Lmart for this project based on demonstrated capability and placed the order through a competitive qualification process — the strongest form of supplier endorsement in capital equipment procurement.

“*"The PHG830 was one of the more demanding vessels in our procurement programme — large diameter, full Inconel 825 wetted surfaces, ASME U Stamp, and a tight schedule. Lmart’s engineering team engaged with the design and inspection requirements from day one rather than waiting for us to drive every decision. The data book they delivered was complete and well-organised. We’ll look at them first on the next requirement in this alloy family."*”

— Technical Director, Process Equipment Engineering, Air Products (paraphrased from project review feedback)

Note: Lmart respects client confidentiality. Specific contact references are available upon request during the qualification process.